Field of the Invention
The present invention relates to image processing for generating an image with the influence of scattered light reduced.
Description of the Related Art
Image capturing of an outdoor distant scene for the purpose of monitoring an airport, a harbor area or the like involves a problem of reduction in sharpness of an image caused by light scattered by airborne fine particles (such as fog, rain, snow, dust and smoke). Image capturing for undersea exploration or the like also poses the same problem caused by light scattered by underwater impurities.
An algorithm for performing processing from a single image based on a dark channel is known as a conventional technology related to image restoration processing which is executed in order to compensate for such image quality degradation in an input image (Refer to U.S. Pat. No. 8,340,461). This technology involves resolving an image into local regions, determining a dark channel from a minimum luminance value of each local region, and determining a transmittance distribution based on the determined dark channel, thereby executing the image restoration processing.
An algorithm for determining a dark channel based on similarity between a pixel of interest and a candidate region is also known (Refer to Japanese Patent Laid-Open No. 2012-221237).
Meanwhile, an algorithm which involves dividing an image into local regions and determining a scattering coefficient thereby to generate a restored image is known as a restoration algorithm without use of a dark channel (Refer to Japanese Patent No. 4807439).